1. Field of the Invention
The present invention relates to a method and system for controlling an optical disc drive, and more specifically, to a method and system for controlling signal gain of the optical disc drive.
2. Description of the Prior Art
With the improvement of computer technologies and the increasing popularity of the Internet, the demand for storing a tremendous amount of information has driven storage media to increase rapidly in storage capacity. Furthermore, the optical disc drive for accessing the information on an optical disc has been tremendously improved with all the efforts. Consequently, the optical disc drive is increasingly important in our daily life. For example, users can access an abundance of information by connecting a computer to the Internet and then storing all the downloaded information onto optical discs. With all of current existing storage medias, the optical disc has featured itself as a low-cost, small-size, low-error-rate, long-storage-time, and high-density storage medium and become the most promising dominant storage medium. Therefore, the corresponding optical storage devices, such as the DVD drives or the DVD burners, are wildly used as standard devices either build-in or accompanied with typical modern computers.
Generally speaking, the optical disc drive accesses data according to optical means, that is, the reading and writing operations include an optical pickup, spindle motor, sled motor, and decoder, encoder IC, etc. The optical pickup, commonly includes a laser diode for reading data or a set of laser diodes for reading and writing data. With respect to the reading process, the optical disc drive sets the output power (also known as the read power) of a laser diode to a desired value. Next, the optical disc drive detects reflected laser light from an optical disc to read data stored on the optical disc. It is well known that the optical disc stores the data utilizing Eight-to Fourteen Modulation signal (EFM signal). This allows the optical disc drive to access data stored on the optical disc by distinguishing a plurality of different intensities of reflected laser light that are generated from the EFM signal. With respect to the writing process, the optical disc drive properly sets the output power (also known as the write power) of the laser diode according to the data waiting to be written onto the optical disc. Accordingly, for reading data from the optical disc or recording data onto the optical disc, the output powers of the laser diode are quite different.
Please refer to FIG. 1. FIG. 1 shows a schematic diagram of an optical disc drive 100 (only components relating to servo control processes are shown) according to the related art. The optical disc drive 100 comprises an optical pickup 110, an auto-power-control (APC) circuit 115, a pre-amp module 120, an analog-to-digital converter (ADC) 130, a compensator module 140, a digital-to-analog converter (DAC) 150, a driver module 160, and an actuator module 170.
The optical pickup 110 outputs a laser light onto an optical disc 101. A plurality of photodiodes of the optical pickup 110 generates a plurality of receiving signals in analog form, such as signals A, B, C, D, E, F, and a front monitor diode signal FMD, according to receiving light beams respectively. The signals A, B, C, D, E, and F are generated according to light beams reflected off the optical disc 101. A front monitor diode (not shown) of the optical pickup 110 senses a portion of laser power for generating the front monitor diode signal FMD so as to adjust the current driving the laser diode such that a desired read or write power is achieved despite temperature change or aging of the laser diode. The APC circuit 115 is utilized to compensate the deviations in the actual laser power level from desirable levels according to the front monitor diode signal FMD.
The pre-amp module 120 comprises amplification circuits for processing the receiving signals A-F so as to generate control signals in analog form, such as the FE (focusing error) signal, the TE (tracking error) signal, and the wobble signal, etc.
The compensator module 140 could be interpreted as a digital signal processor (DSP) in this exemplary embodiment. After the ADC 130 converts the analog servo control signals into digital servo control signals, the compensator module 140 generates a digital compensating signal according to the digital servo control signals. Subsequently, the DAC 150 converts the digital compensating signal into an analog compensating signal. Then, the driver module 160 generates a driving signal according to the analog compensating signal. Thereafter, the actuator module 170 processes the servo control task adequately according to the driving signal.
Please refer to FIG. 2. FIG. 2 is a schematic diagram illustrating different detection signals generated by the optical pickup 110 for a read-detecting signal 210, a first write-detecting signal 220, and a second write-detecting signal 230, having time along the abscissa. The detection signal in a reading process from an optical disc is shown as a read-detecting signal 210. The detection signal in a first writing process for a rewritable optical disc is shown as a 1st write-detecting signal 220. The detection signal in a second writing process for a rewritable optical disc is shown as a 2nd write-detecting signal 230.
The amplitude of the read-detecting signal 210 is much smaller than the amplitude of the first write-detecting signal 220, which results from a higher laser power while performing a writing process. The amplitude of the second write-detecting signal 230 is greater than the amplitude of the first write-detecting signal 220, which means that a higher writing laser power is required after a first writing process on a rewritable optical disc. Therefore, while processing an amplification process on detection signals having different amplitudes from the optical pickup 110 by the pre-amp module 120, signals having higher amplitudes such as the 2nd write-detecting signal 230 may cause undesirable saturation occurrences in circuit operations.